Story highlights

More than 4,500 flights have reportedly been canceled for Friday and Saturday

Shows, classes, church services canceled along parts of East Coast ahead of storm

(CNN)Latest developments:

• Georgia Gov. Nathan Deal issues a state of emergency for 21 counties.

• More than 4,500 flights have reportedly been canceled for Friday and Saturday ahead of the expected storm, according to the flight-tracking website flightaware.com.

• Amtrak also announced a modified schedule in the Northeast because of the impending storm.

• Gov. Tom Wolf has declared a state of emergency in Pennsylvania, joining Tennessee, Maryland, Virginia and North Carolina. "We cannot control the weather, but we can all be prepared for whatever the weather brings us," he told reporters Thursday.

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Communities on the East Coast braced Thursday for what could be the winter's biggest storm yet.

About 75 million people are in the storm's path, with nearly 30 million under blizzard watches or warnings. Severe weather, including tornadoes, could hit Gulf states, and some of the country's most populous cities could see blizzard-like conditions.

There could be winds as strong as 60 mph, coastal storm surges and flooding on top of whatever precipitation will fall. And it could be a lot.

"It's not out of the question that some localized areas receive over 2 feet of fresh snow," CNN meteorologist Taylor Ward said.

Virginia State Police untangled 767 accidents and responded to 392 calls for disabled vehicles Wednesday night and early Thursday. And north of Washington in Beltsville, Maryland, a man walking along U.S. Route 1 in treacherous conditions died after a snowplow hit him, said Maryland State Police Sgt. Christopher Hohenstein.

Commutes turned into hours-long affairs. Many drivers didn't get home until well after midnight.

Even the commander in chief had to reckon with the wintry mix. Video shows President Barack Obama's motorcade using hazard lights Wednesday as it made its slippery way from Joint Base Andrews to the White House. Obama was unable to fly on Marine One because of the weather.

Thursday morning's drive was similarly frustrating, as some icy spots lingered, and commuters left early to allow plenty of time for the ride in.

Hope is to be 'overprepared,' then 'underwhelmed'

This dusting may be nothing, compared with the much larger, more powerful system on the way.

States from Oklahoma east to the Atlantic Coast hunkered down Thursday as ice and snow rolled through. Ward, the CNN meteorologist, warned that 1 to 2 feet of snow could fall "from eastern Kentucky across West Virginia, Virginia, Maryland and into southern Pennsylvania and New Jersey."

Garth Brooks' concerts have been postponed Friday and Saturday at Baltimore's Royal Farms Arena "for the safety of all fans and all personnel involved." The postponement is among dozens of cancellations of shows, classes and more because of the storm.

For many, it's still up in the air what will fall: Little Rock, Arkansas, for instance could see rain, sleet and even snow thunder overnight in addition to heavy snow, according to the National Weather Service.

Tennessee got hit early, with the Knox County Sheriff's Office reporting the death of a 19-year-old man after his car slid off the road Wednesday "due to weather and speeding." North Carolina saw two deaths late Wednesday in crashes along snow-covered roads.

Both states are expecting more bad weather -- with several inches of snow and sleet likely in Knoxville, Tennessee, significant icing in Charlotte, North Carolina, and up to 8 inches of snow in Asheville, North Carolina.

North CarolinaGov. Pat McCrory said his state is doing "everything we can" to get public safety personnel ready in case the worse-case scenarios come true. Several schools, churches and courts around North Carolina had been ordered closed Friday, according to CNN affiliate WRAL-TV. The Panthers Pride Rally scheduled for Friday in Charlotte was canceled.

"Our goal with this potential winter storm ... is to be overprepared and hopefully underwhelmed," McCrory said.

Transportation troubles

More than 3,000 flights have reportedly been canceled for Friday and Saturday ahead of the expected storm, according to the flight-tracking website flightaware.com.

American Airlines said it was canceling all flights Friday in Charlotte and that it would cancel operations in Washington and Baltimore on Saturday.

It also canceled flights Saturday in Philadelphia.

United Airlines announced it would suspend flights at its Washington Dulles International Airport hub and other mid-Atlantic airports starting Friday afternoon.

Amtrak also announced a modified schedule in the Northeast because of the storm, while the Washington Metropolitan Area Transit Authority (Metro) said the Metrorail system would be closed all day Saturday and Sunday.

"This is not a storm that anyone should take lightly, and I would urge all residents to plan to get to a safe place before the storm arrives Friday afternoon," said Metro General Manager/CEO Paul J. Wiedefeld.

"The actions we are taking today are all in the interest of our customers' and employees' safety, and will help us return to service once the storm passes and the snow is cleared."

Shelves cleared around Washington area

Strong gusts, combined with accumulating snow or ice, could knock out power to many amid subfreezing temperatures -- a prospect that Washington's mayor called "my biggest concern."

Nearly 2 feet of snow fell in February 2010's "Snowmageddon" storm, which cut power to hundreds of thousands in the region.

For the weekend storm to be of historic proportions, snow accumulations in Washington would have to top 28 inches. That would exceed the calamitous "Knickerbocker Storm" of 1922, which dumped 28 inches and killed nearly 100 people when the roof of a theater by that name collapsed under the weight of snow.

As of midday Thursday, the greater Washington metro area -- from Fredericksburg, Virginia, northward, incorporating all of Maryland -- was under a blizzard warning.

"Heavy snow and blowing snow will cause dangerous conditions and will be a threat to life and property," the National Weather Service warned. "Travel is expected to be severely limited if not impossible during the height of the storm Friday night and Saturday."

Bowser, Washington's mayor, has declared a state of emergency, closed schools for Friday and given the OK to move any vehicle found on a snow emergency route.

Washington appears to be in the storm's bull's-eye, but most of the Mid-Atlantic states -- and a few points west -- will also take a hit. There's more uncertainty for Philadelphia and New York, though the latter city's mayor has ordered some 4,800 sanitation workers charged with clearing streets to go on to 12-hour shifts Friday.

The forecast there calls for snow to start falling overnight Friday, with 7 to 15 inches possible by the end of the weekend.

.@NYCSanitation is ready: workers have been assigned to two 12-hour shifts starting Friday at 7 AM, with 2,400 workers per shift. #SafeNYC